Lithography is a very important process in semiconductor manufacturing. It is a process of transferring a series of chip patterns on a mask to a corresponding layer of a silicon wafer through exposure. It is considered as the core step in the large-scale manufacture of integrated circuits. A series of complex and time-consuming lithography processes in semiconductor manufacturing are mainly accomplished by corresponding lithography machines.
In the process of exposure of the lithography machine, the organic solvent in the photoresist on the silicon wafer surface will be volatilized slowly after being heated, and the volatilized organic matter will adhere to the lens on the lower surface of the object lens. The adhesive matter directly affects the light transmittance in the object lens, and then affects the imaging quality of the product. Because the last lens on the lower surface of the object lens is very close to the surface of the silicon wafer, volatilized organic matter will easily adhere to the surface of the lens.
As illustrated in FIG. 1, the existing lithography machines mostly use the method of mounting an object lens protective film 102 on the lens base 101 of the lower surface of the object lens to prevent the organic matter from contaminating the lens. However, the protective film based anti-contamination device and method still have many shortcomings. Firstly, the normal service life of the protective film is determined by the energy of the transmitted light. Even in normal use, under the irradiation of 365 nm and 436 nm ultraviolet light, the service life of the protective film can only withstand the energy of 500000 J/cm2, and the replacement frequency is once per one to two months. Secondly, the price of the protective film is very high. By calculating according to the price of each protective film which is CNY 1500, the normal loss is CNY 9000-18000 per year. Frequent replacement increases the use cost. In addition, because the distance between the surface of the silicon wafer and the lower surface of the object lens is only 40 mm, it is difficult to replace the protective film, which is easy to burst in the process of replacement; in addition, because the thickness of the film is very small, the change of external pressure will also cause the rupture of the protective film, the abnormal damage rate is up to 15% at present. If the protective film is broken inadvertently in the process of use, it will cause contamination of the lens which is conducting imaging process, and in serious cases, the imaging process fails. More importantly, it has been proved that, due to the limitation of the mounting structure, the protective film cannot completely prevent the organic matter volatilized from the photoresist from contaminating the lens; even, because the protective film cannot completely guarantee that the volatilized organic matter is removed, there may be contaminated parts in the whole lithography machine, such as the lens inside the object lens cavity, the upper surface lens, the surface of the silicon lens and the mask, which have requirements on cleanness. Because the lithography machine is high-precision equipment, more serious losses will be caused to users.
Therefore, a device and/or method for better preventing organic matters in photoresist from being volatilized and contaminating lenses are needed.